Synthesis and Physical Characterization of thin silicondioxide (SiO$_{2})$ layers with very high densities of E' centers

E' centers are paramagnetic (s$=$1/2) electronic states which are due to silicon dangling bonds in a-SiO$_{2}$ [1]. E' centers are able to trap electric charge, which can be detrimental to the performance of silicon based electronic devices. Therefore, most previous studies of E' centers have focused on a-SiO$_{2}$ layers with low E' center densities and material preparation techniques that allow to minimize it. Here, we present a study aiming at the opposite, the question of how E' center densities in a-SiO$_{2}$ can be maximized and whether E' centers in higher densities still exhibit similar spin dynamics (relaxation rates) in comparison to SiO$_{2}$ with low E' center densities. This study has been motivated by the need for a dielectric material containing very high spin densities as needed for single spin detection techniques. It is shown in this study that E' centers can be created at densities above $\sim$ 10$^{19}$ cm$^{-3}$ through exposure of a thin thermal oxide sample to an rf plasma containing Ar at low pressure. Most of the E' centers were found within 20 nm to 30 nm of the SiO$_{2}$ surface. While the high E' center densities can be annealed completely at 300 $^{\circ}$C, they are very stable at room temperature. Spin relaxation time measurements show that $T_{2}$ of high density E' centers does not strongly depend on temperature and $T_{1}$ is $\sim$ 600$\mu $s at 5K with an increase towards lower densities [1]. At room temperature$ T_{1}$ is $\sim$ 160$\mu $s, which agrees well with values found in literature for E' centers at low densities [2].\\[4pt] [1] J. G. Castle, \textit{J. Appl. Phys}. \textbf{36}, 124 (1965).\\[0pt] [2] S. S. Eaton, \textit{J. of Mag. Res. Series A, }\textbf{102}, 354-356 (1993).